The invention relates to improvements in methods of and in apparatus for manipulating sheets, and more particularly to improvements in methods of and in apparatus for manipulating photosensitive sheets, e.g., in photographic processing laboratories.
The processing of exposed photographic films and the making of prints on photographic paper involves the transport of such sheet- or web-like materials at different speeds. This creates problems, particularly in connection with the advancement of paper sheets in the developing machine of a photographic processing laboratory. For example, the speed of paper sheets through the developing, fixing and rinsing baths of a developing machine is less than the speed of sheets in the copying machine. Thus, if the speed of sheets in the developing machine were to be raised to match the speed of such sheets in the copying machine, the length of the path for the sheets in the developing machine would have to be increased accordingly (in order to ensure that each sheet is contacted by the developing and other solutions for a required internal of time). This is not always possible because any lengthening of the path for exposed sheets of photographic paper through the developing machine would entail a corresponding increase in the bulk and space requirements of such machine. On the other hand, the space is at a premium in a so-called minilab, e.g., a processing laboratory which is set up to develop an exposed photographic film, to copy selected frames of the exposed and developed film onto photosensitive paper, to develop the thus exposed photographic paper, to sever the developed paper into discrete prints and to collate the prints with the corresponding film frames so that the order can be picked up by a customer within 60 minutes (or even less) from the time of delivery.
Commonly owned patent application Ser. No. 07/942,431 of Erich Nagel (filed Sep. 9, 1992 for "Apparatus for converting a file of successive sheets into plural rows of sheets") discloses an apparatus which can be used in a photographic processing laboratory to permit the development of a larger number of sheets of exposed photosensitive paper without increasing the bulk and space requirements of the developing machine for exposed photosensitive paper. This is accomplished in that the apparatus is designed to convert a single file or row of exposed but undeveloped sheets into plural rows, and the plural rows are caused to advance through the developing machine. The apparatus of Nagel employs a carriage which can be moved sideways to stagger the oncoming sheets and to thus convert a single row of oncoming sheets into plural rows of sheets which are ready to be introduced into the developing machine. The disclosure of the application of Nagel is incorporated herein by reference.
The baths of a developing machine contain small particles of contaminants, e.g., fragments of sheet advancing rolls. The floating particles descend onto and tend to adhere to the peripheral surfaces of rolls in the developing machine while the machine is idle. As a rule, the thus gathered accumulations of particles are removed from the peripheral surfaces of the rolls when the developing machine is restarted because the oncoming sheets rub against and remove such accumulations of impurities. In other words, the developing machine is automatically cleaned when in use so that the particles of foreign matter cannot gather on the exposed sheets in numbers and sizes such that they would affect the quality of the exposed and developed images. However, if an apparatus of the type disclosed in the patent application Ser. No. 07/942,431 of Nagel is used extensively for the advancement of plural rows of sheets, those portions of the rolls in the developing machine which are located between neighboring rows are likely to gather entire layers of impurities. Such layers are harmless as long as the apparatus continues to process several rows of relatively narrow sheets. However, if the same apparatus is thereupon used for the advancement of relatively wide sheets which cannot form two or more rows because the width of the path for the sheets is barely sufficient to accommodate a single row of relatively wide sheets, the accumulations of solid impurities on the rolls of the developing machine are removed by the foremost (wide) sheets of a single row of sheets. The thus removed layers of impurities are readily visible on the finished prints in the form of elongated dark strips or streaks which render the prints useless or, at the very least, detract considerably from their appearance.
Attempts to avoid the deposition of dark strips on the foremost sheets of a fresh row of sheets of photographic paper or other photosensitive material have met with limited success. For example, it was proposed to install automatic cleaning units which employ brushes and are set in operation before the developing machine is restarted or before the machine is restarted to advance relatively wide sheets subsequent to long-lasting transport of plural rows of relatively narrow sheets. It was also proposed to advance a series of so-called cleaning sheets through the developing machine prior to advancement of exposed photosensitive sheets so that the specially designed cleaning sheets remove layers of impurities from the rolls in the developing machine before the latter is put to renewed use but for the development of a single row of wide sheets following a long-lasting use for the development of plural rows of narrower sheets. Such additional equipment is expensive and contributes to the bulk of the developing machine. Moreover, its cost does not justify the installation in a developing machine which is used primarily for the development of relatively wide sheets forming a single row, or primarily for the development of narrower sheets forming several rows.